Portuguese Beef and Onions (Bifes De Cebolada)

A recipe that I found at recipes4us.co.uk and am posting this for ZWT Spain/Portugal region. I think this would be nice served over pasta, rice or with mashed potatoes. This isn't a spicy dish, so if you are wanting a little zip to the beef/veggie mix, feel free to add red pepper flakes or cayenne pepper to taste.